Checking and comparing the backs of cards is a good indicator if you look for fakes. Backs from i.e. Chinese counterfeits tend to look blurry and have various details which are off from real cards. But there are some significant differences between old and modern cardbacks as well and if you are checking for rebacks, be sure to check the backs aswell. Many of them were done on modern card backs and it is one of the number one things which stand out if you trying to spot one.
Old vs. Modern Cardframe
Below is a quick comparsion between old and new card frames. As you can see the older backs are more grainier and have a higher contrast at all. If you look into the brown center area you can see something I call “clouding”, it is much more visible on old backs. But see yourself:
And of course you want to see some fake backs here to, this time I did a scan. Here is a comparsion between a chinese counterfeit and an original modern magic card. I think the differences are quite obvious. These are some of the better backs they do. You can find tips on how to spot fakes by checking the details in some of the other articles. One of the most recommended ones is the green dot check.